Wireless communication system

ABSTRACT

A wireless communication system base station, and a remote radio head (RRH) and a computer-implemented synchronization method for the wireless communication system base station. The RRH is communicably coupled to a baseband unit (BBU) of the wireless communication system base station through a network, and the BBU processes and transmits downlink data to the RRH. The RRH includes: a time-delay measurement unit for measuring a time-delay for the downlink data to arrive at the RRH from the BBU; and a time-delay notification unit for notifying from the RRH to the BBU of time-delay data on the time-delay measured by the time-delay measurement unit, wherein the time-delay data is used to advance the starting time for the BBU to process and transmit the downlink data by an amount of time obtained based on the time-delay data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority from U.S.application Ser. No. 13/392,887, which is a U.S. National Phaseapplication that claims priority from International ApplicationPCT/EP2010/061960, filed Aug. 17, 2010, which in turn claims priorityfrom Chinese Patent Application No. 200910170969.2, filed on Aug. 31,2009. The entire contents of all of these applications are incorporatedherein by reference.

BACKGROUND

The present invention generally relates to wireless communicationsystems, specifically, to data transmission synchronization between abaseband unit and a remote radio head of a wireless communication systembase station in wireless access network.

The latest generations of wireless communication systems use remoteradio head (RRH) technology in a distributed base station architecturewhere all radio related functions are included in a Remote Radio Headwhich can be installed next to the antenna and which allows for greaterdistances between the RRH and antenna of a base station (BS) and thebaseband unit (BBU) of the BS, reducing set-up and operational costs.The BS can centralize multiple BBUs and deploy the RRHs and the antennaein a distributed manner. FIG. 1 shows an architecture supporting dynamicRRH stream-switching for different BBU boards, wherein a plurality ofBBU boards serve as a resource pool to provide processing resources forRRHs in an on-demand manner.

In digital communication network, reliably transmitting audio, video anddata requires accurate timing and synchronization. In traditionalimplementation of communication between a BBU and a RRH, the BBU and RRHof a base station are connected directly through a TDM (time divisionmultiplexing) link, on which data is transmitted at clock of the TDMlink, and thus transmission time-delay is generally fixed andtransmission jitter is not generated. Furthermore, processing time-delayis also generally fixed due to the use of computing platforms based onDSP/FPGA, (Digital Signal Processing/Field Programmable Gate Arrays)etc., which do not have operating system.

Next generation wireless access network architecture commonly adoptstime division duplex (TDD) wireless communication system, for which datatransmission between a BBU and a RRH is based on a packet switchingnetwork, such as Ethernet or Infiniband, and switch, and thereby datatransmission time-delay is generally not fixed and transmission jittermay occur. Due to the use of computing and transmitting resource poolbased on open IT architecture, processing time-delay is not fixed underthe influence of operation system (e.g. task scheduling, etc.).

SUMMARY OF THE INVENTION

The present invention provides a wireless communication system basestation and data transmission synchronization method thereof (as definedin the appended claims, to which reference should now be made).

In one aspect, the present invention provides a remote radio head (RRH)of the wireless communication system base station, which is communicablyconnected to a baseband unit (BBU) of the wireless communication systembase station through a network, wherein the BBU is used to process andtransmit downlink data to the RRH, said RRH further comprising: atime-delay measurement unit for measuring a time-delay for the downlinkdata to arrive at the RRH from the BBU; a time-delay notification unitfor notifying the BBU of time-delay data on the time-delay measured bythe time-delay measurement unit from the RRH, said time-delay data beingused to advance a starting time for the BBU to process and transmit thedownlink data by an amount of time obtained based on said time-delaydata.

In another aspect, the present invention provides a wirelesscommunication system base station, which comprises a remote radio head(RRH) and a baseband unit (BBU) which are communicably connected througha network, wherein the BBU is used to process and transmit downlink datato the RRH, said wireless communication system base station furthercomprising: a time-delay measurement unit in the RRH for measuring atime-delay for the downlink data to arrive at the RRH from the BBU; atime-delay notification unit in the RRH for notifying the BBU oftime-delay data on the time-delay measured by the time-delay measurementunit from the RRH; a synchronization unit in the BBU for advancing astarting time for the BBU to process and transmit downlink data by anamount of time obtained based on the time-delay data notified by thetime-delay notification unit.

In another aspect, the present invention provides a synchronizationmethod for data transmission of wireless communication system basestation that comprises a remote radio header (RRH) and a baseband unit(BBU) communicably connected through a network, wherein the BBU is usedto process and transmit downlink data to the RRH, said methodcomprising: measuring a time-delay for the downlink data to arrive atthe RRH from the BBU; notifying the BBU of time-delay data on themeasured time-delay from the RRH; advancing a starting time for the BBUto process and transmit the downlink data by an amount of time obtainedbased on the notified time-delay data.

The present invention can reduce or even eliminate RRH receptiontime-delay caused by BBU processing time-delay and data transmissionjitter by measuring the time-delay for the downlink data frame to arriveat the RRH of the base station whereby correcting the timing pulse forstarting downlink data processing and transmission on the BBU side.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other objects, features and advantages of thepresent invention will become more apparent from the detaileddescription of the embodiments of the present invention shown in theaccompanying drawings, in which the like or the same reference numbersare used to indicate the like or the same elements, or parts in theembodiments of the present invention.

FIG. 1 schematically shows an architecture in which the technicalsolution of the present invention can be implemented;

FIG. 2 schematically shows a partial structure of a wirelesscommunication system base station and the operation manner thereof;

FIG. 3 schematically shows a partial structure of a wirelesscommunication system base station according to an embodiment of thepresent invention, and the operation manner thereof;

FIG. 4 schematically shows the variation of the baseband processingpulse according to an embodiment of the present invention;

FIG. 5 schematically shows the circuit of the time-delay measurementunit according to an embodiment of the present invention; and

FIG. 6 schematically shows the flowchart of the method according to anembodiment of present invention.

DETAILED DESCRIPTION

Hereinafter, the implementation of the present invention will bedescribed in detail with reference to the drawings, which showembodiments of the present invention. However, the present invention canbe implemented in various ways, and is not conceived to be limited tothe disclosed manners. Parts and details that are not directly relevantto the contents of the present invention are omitted in the descriptionand drawings, so that the content of the present invention can behighlighted, and those skilled in the art can understand the scope ofthe present invention more clearly.

First, a reference is made to FIG. 1 showing the architecture of awireless communication system base station in which the technicalsolution of the present invention can be implemented. The base stationshown comprises several remote radio heads (RRH) and several centralizedbaseband units communicably connected to the RRHs through a network (apacket-switch network, such as, Ethernet-based or Infiniband-basednetwork). Through a switch (generally, near the baseband unit side), anyRRH can be connected to any BBU to form an uplink or downlink. The RRHis responsible for converting digital data received from the BBU to RFcarriers for radio transmission and vice versa from received radiosignals. The RRH receives uplink data from a mobile communicationterminal (not shown) through functional components, such as A/Dconverter, etc., and then transmits the data to the BBU for processing;the RRH receives downlink data from the BBU through the network, andthen transmits the downlink data to the mobile communication terminalthrough functional components, such as D/A converter, etc.

FIG. 2 schematically shows a partial structure of the wirelesscommunication system base station and the operation manner thereof. Inthe wireless communication system base station (which is also referredto as base station hereinafter) shown in FIG. 2, only one remote radiohead (which is also referred to as RRH hereinafter) and one basebandunit (which is also referred to as BBU hereinafter) are illustrated,wherein the RRH and the BBU are communicably connected through a packetswitching network, (such as Ethernet) and communicate data in a TDDcommunication manner.

As shown in FIG. 2, the RRH comprises a transceiver unit 100, a pulsegenerator 150, an analog to digital converter (which is also simplifiedas A/D hereinafter) 130 and a digital to analog converter (which is alsosimplified as D/A hereinafter) 140. The BBU comprises a data processingunit 200 and a timer 250.

The transceiver unit 100 of the RRH is used to receive and transmit databetween the A/D 130 and the BBU and between the D/A 140 and the BBU, andfurther comprises an uplink unit 110 and a downlink unit 120, whereinthe uplink unit 110 is used to receive data from the A/D 130, processthe received data and transmit the processed data to the BBU over anetwork; the downlink unit 120 is used to receive downlink data from theBBU over the network and transmit the received downlink data to the D/A140.

The data processing unit 200 of the BBU is used to receive and processthe uplink data from the RRH, and to process and transmit the downlinkdata to the RRH. The data processing unit 200 further comprises anuplink data processing unit 210 for receiving and processing the uplinkdata from the RRH and a downlink data processing unit 220 for processingand transmitting the downlink data to the downlink unit 120 of the RRH.

The base station can be switched between uplink mode and downlink modein operation. When the base station is in uplink mode, its communicationhardware circuits serve for the BBU to receive data, i.e. uplink datafrom a mobile communication device (not shown). The A/D 130 receivesanalog signals from the mobile communication device, converts thesignals into digital signals, and then transmits them to the transceiverunit 100 of the RRH. The transceiver unit 100 processes the digitalsignals, for example, groups and encapsulates the digital signals intoframes, and then transmits them to the BBU over a packet switchingnetwork for further processing by the BBU's data processing unit 200.When the base station is in downlink mode, its communication hardwarecircuits serve for the BBU to transmit data, i.e. the downlink data, tothe mobile communication device. The BBU transmits the data having beenprocessed by the data processing unit 200 to the transceiver unit 100 ofthe RRH over the packet switching network. The transceiver unit 100processes the received data, for example, restores data from the frames,and then transmits the processed data to the D/A 140, which converts thedata into analog signals and then transmits them to the mobilecommunication device.

The pulse generator 150 is used to issue timing pulses for variouscircuit modules of the RRH, including uplink pulse T_(UL), downlinkpulse T_(DL) and switching pulse T_(s).

In uplink mode, the uplink pulse T_(UL) is used to trigger the A/D 130to receive uplink data from the mobile communication device. In downlinkmode, the downlink pulse T_(DL) is used to trigger the D/A 140 totransmit downlink data to the mobile communication device. The switchingpulse T_(s) is used to trigger switching between the uplink mode and thedownlink mode. In downlink mode, after the switching pulse T_(s) isissued from the pulse generator 150, the D/A stops transmitting data tothe mobile communication device, and the hardware circuits of the RRHare switched to uplink data processing state. In uplink mode, after theswitching pulse T_(s) is issued from the pulse generator 150, the A/Dstops receiving data from the mobile communication device, and then thehardware circuits of the RRH are switched to downlink data processingstate.

It should be appreciated by those skilled in the art that, the timingpulses which can be provided by the pulse generator 150 are much morethan those pulses mentioned above, and those pulses mentioned above canalso be generated by different pulse generators which are physicallydiscrete, for which no further description will be given herein.

The timer 250 can issue timing pulses for various circuit modules of theBBU, including timing baseband processing pulse T_(DP). The dataprocessing pulse T_(DP) is used to trigger the operation of the downlinkdata processing unit 220 of the data processing unit 200, i.e. to startprocessing the downlink data to be transmitted to the RRH, for example,encapsulating data into frames and transmitting the downlink data frames(which is simplified as downlink frame hereinafter) to the RRH.

It should be appreciated by those skilled in the art that a downlinkframe consists of a frame header and a frame body, and the frame bodymay comprise one or more data samples, each of which is data withcertain length, for example, 16 bits or 32 bits.

The transceiver unit 100 of the RRH receives downlink frames from theBBU, and it may take some time for the RRH to receive a downlink framecompletely, and the time is called downlink frame duration. Similarly,the uplink data frame transmitted from the RRH to the BBU (which issimplified as uplink frame hereinafter) comprises a frame header and oneor more data samples, and the time required to transmit an uplink framecompletely is called uplink frame duration.

The cycle from the beginning of a downlink frame to the end of an uplinkframe constructs an uplink-downlink period. The length of theuplink-downlink period=downlink frame duration+time required to switchbetween downlink mode and uplink mode+uplink frame duration. In aconfiguration, for example, the uplink-downlink period is 10 ms, whereinthe downlink frame duration is 4.5 ms, the time required to switchbetween DL and UL is 0.5 ms, and the uplink frame duration is 5 ms.

The frequency of the downlink pulse T_(DL) is set to match theuplink-downlink period. For example, if the uplink-downlink period is 10ms, then the frequency of T_(DL) is 100 Hz, i.e. the pulse generator 150issues a downlink pulse T_(DL) every 10 ms.

In normal situation, the timing mechanisms in RRH and BBU make thedownlink frame synchronized between the BBU and the RRH, that is, thedownlink frame is synchronized with the downlink pulse T_(DL) and theswitching pulse T_(S). In other words, when a downlink pulse T_(DL) isissued, the first data sample of a downlink frame should have alreadyarrived at the transceiver unit 100 and been received by the transceiverunit 100; when a switching pulse T_(s) is issued, the last data sampleof the downlink frame should have already arrived at the transceiverunit 100; otherwise, the whole downlink frame would not be transmittedto the mobile communication device by the D/A 140 during the currentperiod.

It should be appreciated by those skilled in the art that the time forthe downlink frame data sample to arrive at the transceiver unit can beinfluenced by both downlink data processing and transmission time-delayof the data processing unit 200 (processing time-delay) and transmissionline jitter. For example, the processing time-delay of the dataprocessing unit 200 of the BBU may render that the first data sample ofthe downlink frame arrives at the transceiver unit after a delay.

Referring to FIG. 3 below, various implementations of the presentinvention will be described. FIG. 3 shows a partial structure of thewireless communication system base station according to one embodimentof the present invention and the operation manner thereof. Thecomponents shown in FIG. 3 are mostly the same as those of FIG. 2,except that FIG. 3 also comprises a time-delay measurement unit 180 anda time-delay notification unit 170 in the RRH, and a synchronizationunit 290 in the BBU.

The RRH shown in FIG. 3, as an embodiment of the RRH of the wirelesscommunication system base station according to the present invention, iscommunicably connected to the BBU comprising the synchronization unit290 through a network, so as to construct a wireless communicationsystem base station according to an embodiment of the invention. The RRHand the base station will be described in detail with reference to thedrawings below.

The time-delay measurement unit 180 is used to measure the time-delayfor the downlink data to arrive at the RRH from the BBU. The time-delayfor the downlink data to arrive at the transceiver unit and thus the RRHfrom the BBU can be measured by setting a timer in the RRH to record thetime that the downlink data should arrive at the transceiver unit 100 ofthe RRH and the time that the downlink data actually arrived at thetransceiver unit respectively, and then calculating the differencebetween the two times. The particular implementation of the time-delaymeasurement unit will be further described with reference to FIG. 5below.

The time-delay notification unit 170 is used to notify the BBU oftime-delay data on the time-delay measured by the time-delay measurementunit 180. Especially, the time-delay notification unit 170 may receivetime-delay data on the time-delay for downlink data to arrive at the RRHfrom the BBU, process the time-delay data appropriately, for example,encapsulate it into a frame, and then transmit the frame to the BBU ingaps for transmitting the uplink frame. According to one embodiment ofthe present invention, as shown on the upper half of FIG. 3, thetime-delay notification unit 170 may, upon switched from downlink modeto uplink mode, transmit time-delay data to the BBU just following thetransmission of an uplink frame by the uplink unit. To facilitateprocessing and transmitting the time-delay data, according to oneembodiment of the present invention, the time-delay notification unitmay be provided in the uplink unit 110 of the RRH, or alternatively, theuplink unit can be reconstructed to have the function of the time-delaynotification unit, which is easy to implement for those skilled in theart, and thus no further description will be given herein.

The synchronization unit 290 is used to advance the starting time forthe BBU to process and transmit downlink data by an amount of timeobtained based on the time-delay data T_(D) notified by the time-delaynotification unit 170.

For example, upon receiving (e.g., through uplink unit 110) the RRHtime-delay data from the RRH according to a predetermined protocol, thedata processing unit 200 (e.g., the uplink data processing unit 210) ofthe BBU processes the time-delay data (e.g., restores the time-delaydata from a frame), and then transmits it to the synchronization unit290. The synchronization unit 290 takes the time-delay data as anadjustment parameter, for example, to make the time for the dataprocessing unit 200 to thereafter process and transmit the downlink databe advanced by an amount of time-delay indicated by the time-delay data,so that the next downlink frame can arrive at the RRH earlier.

It should be appreciated by those skilled in the art that, the measuredframe header time-delay T_(d1) is often due to the processing time-delayfor the data processing unit 200 of the BBU to process the downlinkdata, and the frame trailer time-delay T_(d2) characterizes the sum ofthe frame header time-delay T_(d1) and the jitter time-delay fortransmission of a data frame. Therefore, generally speaking, forexample, if T_(d1)=T_(d2), it is often indicated that there has nojitter in the data transmission of the base station; on the other hand,if T_(d2) is significantly larger than T_(d1), it is indicated thatthere has obvious jitter in data transmission. In implementation of thepresent invention, clock can be corrected based on different clockcorrection algorithms, so as to adjust the triggering or starting timefor the data processing unit 200 to process and transmit the downlinkdata, that is, to advance the triggering or starting time for the dataprocessing unit 200 to process and transmit the downlink data. Accordingto one embodiment of this invention, the larger one of T_(d2) and T_(d1)can be used as a reference parameter to perform the above adjustment.For example, if T_(d2) is larger than T_(d1), the starting time for thedata processing unit 200 to process and transmit the downlink data canbe advanced by an amount of time T_(d2).

Considering that jitter is rapidly-varying, the whole system may easilyget into an unstable state if performing the adjustment based on T_(d2)every time. According to an embodiment of the present invention, forexample, if there is an insignificant difference between T_(d1) andT_(d2), merely taking T_(d1) as the reference parameter to perform theadjustment is also possible, e.g. advancing the starting time for thedata processing unit 200 to process and transmit the downlink data by anamount of time T_(d1).

Of course, in practice, a more complicated reference parameter can beused for adjustment depending on the specific ranges of T_(d1) andT_(d2). According to an embodiment of the present invention, forexample, the sum of the average of (T_(d2)−T_(d1)) over a period of timeand the current T_(d1) can be used as the reference parameter to performthe adjustment. For example, the sum of the average of (T_(d2)−T_(d1))for each of N periods prior to the current uplink-downlink period andthe current T_(d1), can be used as the reference parameter to performthe adjustment, wherein N is an integer larger than 1.

According to one embodiment of the present invention, thesynchronization unit can be implemented with a timing correction unit inthe conventional technology, which may generate a time-delayed clockpulse to replace a timing baseband processing pulse for triggering thedownlink data processing unit 200 to start the downlink data processingand transmission, based on said timing baseband processing pulse and thetime-delay data, so as to advance the starting time for the downlinkdata processing unit to process and transmit the downlink data by theamount of time mentioned above. Referring to FIG. 4, FIG. 4schematically shows the variation of the timing baseband processingpulse for triggering the downlink data processing unit to process andtransmit the downlink data after the use of the timing correction unitaccording to the embodiment of the present invention. The lower left ofFIG. 4 shows the timing baseband processing pulse before the correction,and the lower right shows the time-delayed timing baseband processingpulse, i.e. the timing baseband processing pulse adjusted by the timingcorrection unit. Comparing the timing baseband processing pulse on thelower left and the time-delayed timing baseband processing pulse on thelower right of FIG. 4 using the same high frequency system clock pulseshown over them as a reference, it can be seen that, the time-delayedtiming baseband processing pulse has a higher frequency, and thus thestarting time for downlink data processing unit 200 to process andtransmit the downlink data triggered by the time-delayed timing basebandprocessing pulse will be advanced.

The timing correction unit 292 according to an embodiment of the presentinvention is shown in FIG. 3, wherein the timing correction unit 292takes the timing baseband processing pulse T_(DP) output from the timer250 as one input and the time-delay data T_(D) serving as the adjustmentparameter as another input, and outputs a time-delayed timing basebandprocessing pulse T_(DP′). Those skilled in the art of electroniccircuits may understand that, such timing correction unit 292 can be acircuit structure easily realized in conventional technology and thus nofurther description will be given herein. It should be noted that,although the timing correction unit 292 shown in FIG. 3 takes the timingbaseband processing pulse T_(DP) as one input, in a practicalimplementation, as well known by those skilled in the art, thetime-delayed timing baseband processing pulse T_(DP′) output by thecorrection unit also can be an input of the timing correction unit so asto form a feedback, which will not be described in detail herein.

Next, the embodiment of the time-delay measurement unit of the presentinvention will be further described. In the case of using the pulsegenerator 150 in the RRH to generate the downlink pulse T_(DL) fortriggering the downlink data transmission of D/A 140 to the mobilecommunication device, a frame header time-delay measurement means 181 ofthe present invention can be used to obtain the time that the D/A 140begins to transmit downlink data to the mobile communication device byobtaining the time of the downlink pulse; in addition, since it is thefirst data sample of the downlink frame the downlink unit 120 receivesfrom the BBU, the time for the first data sample of the downlink frameto arrive at the RRH can be obtained from the downlink unit. Thus, withtwo timers and one subtracter, the frame header time-delay measurementmeans can be realized as a means for measuring the time differencebetween the generating time of the downlink pulse T_(DL) and the timewhen the first data sample of the downlink frame of the BBU arrives atthe downlink unit. Similarly, the frame trailer time-delay measurementmeans 182 can be further simply realized as a means for measuring asecond time difference between the generating time of the switchingpulse Ts and the time when the last data sample of the downlink frame ofthe BBU arrives at the downlink unit.

FIG. 5 illustratively shows a circuit implementation of a time-delaymeasurement means according to an embodiment of the present invention.As shown in FIG. 5, the frame header time-delay measurement means 181comprises a counter 510, a subtracter 520, and a divider 530, whereinthe counter takes the downlink pulse T_(DL), a notification from thedownlink unit indicating that the first data sample of the downlinkframe has arrived at the downlink unit 120, and a beat clock pulseCLK_(DA) as its inputs, wherein the beat clock pulse CLK_(DA) is a beatclock pulse provided by the system clock for the digital-to-analogconversion of the data samples of the downlink data one by one by theD/A 140, which is a high frequency pulse as compared to the pulsesT_(DL) and T_(UL), and can also be generated by the same pulse generator150.

The counter 510 continually counts the clock pulses CLK_(DA). As shownin FIG. 5, when a downlink pulse T_(DL) is issued, the counter 510 istriggered to output the current count value C₁₁; for example, anotification issued by the downlink unit 120 indicating that the firstdata sample of the downlink frame has arrived at the downlink unit 120triggers the counter 510 to output the current count value C₁₂; and theabsolute value of the difference between C₁₁ and C₁₂ is obtained throughthe operation of the subtracter. As shown with“/F_clk_(DA)” in block530, the absolute value is divided by the frequency F_clk_(DA) of thebeat clock pulse CLK_(DA) to get the frame header time-delay T_(d1). Theabove circuit can be expressed as:

T _(d1) =|C ₁₁ −C ₁₂ |/F_CLK_(DA)

where C₁₁ is the current count value of the counter 510 when the T_(DL)is issued, C₁₂ is the current count value of the counter 510 when thefirst data sample of the downlink frame arrives, and F_CLK_(DA) is thefrequency of the beat clock pulse CLK_(DA).

Another circuit (not shown in detail) with the same function formed bycounter, adder and divider can be used to calculate the frame trailertime-delay T_(d2)=|C₂₁−C₂₂|/F_CLK_(DA). Where C₂₁ is the current countvalue of the counter when the switching pulse Ts arrives; C₂₂ is thecurrent count value of the counter when the last data sample of thedownlink frame arrives.

The above circuits for calculating T_(d1) and T_(d2) are merelyillustrative, and various variations are also possible, for example, thecircuits for calculating T_(d1) and T_(d2) contain respective countersrespectively, but may share a subtracter and a divider; or even thesetwo counters can be a same counter. It is obvious for those skilled inthe art to implement the time-delay measurement means 180 in variousother manners.

Various implementations of the wireless communication system basestation according to the present invention have been described withreference to FIGS. 1-5 above. Those skilled in the art may understandthat, other implementations that are not set forth explicitly but can bederived from the above description can also be obtained from the abovevarious embodiments.

With the same inventive conception, the present invention also providesa data transmission synchronization method for wireless communicationsystem base station. FIG. 6 schematically shows the flowchart of themethod according to an embodiment of the present invention.

The wireless communication system base station to which the datatransmission synchronization method according to the embodiment of thepresent invention is applied comprises a remote radio head (RRH) and abaseband unit (BBU) communicably connected through a network, whereinthe BBU is used to process and transmit downlink data to the RRH. Asshown in the figure, the data transmission synchronization method of thepresent invention comprises the following steps: beginning at step 610,first of all, measuring a time-delay for the downlink data to arrive atthe RRH from the BBU; at step 620, notifying from the RRH to the BBU oftime-delay data T_(D) on the measured time-delay; at step 630, advancingthe starting time for the BBU to process and transmit the downlink databy an amount of time obtained based on the notified time-delay data.

According to an embodiment of the present invention, the time-delay forthe downlink data to arrive at the RRH from the BBU can be measured inthe following manner: measuring the time difference T_(d1) between thetime when the digital-to-analog (D/A) converter contained in the RRHbegins to transmit downlink data to the mobile communication device andthe time when the first data sample of the data frame of the downlinkdata arrives at the RRH, which is also called a first time differenceherein. Thus, the first time difference T_(d1) is contained in thetime-delay data T_(D) on the measured time-delay notified from the RRHto the BBU at step 620; and the amount of time equals to the first timedifference T_(d1).

According to an embodiment of the present invention, the time-delay forthe downlink data to arrive at the RRH from the BBU can be measured inthe following manner: measuring the time difference T_(d2) between thetime when the wireless communication system base station switches fromdownlink mode to uplink mode and the time when the last data sample ofthe data frame of the downlink data arrives at the RRH, which is alsocalled a second time difference herein. Thus, besides the first timedifference T_(d1), the second time difference T_(d2) is contained in thetime-delay data T_(D) on the measured time-delay notified from the RRHto the BBU at step 620.

According to an embodiment of the present invention, in the case of thetime-delay data T_(D) contains the first time difference T_(d1) and thesecond time difference T_(d2), at step 630, the starting time for theBBU to process and transmit the downlink data is advanced by an amountof time that equals to the larger one of the first time differenceT_(d1) and the second time difference T_(d2), based on the first timedifference T_(d1) and the second time difference T_(d2) of the notifiedtime-delay data.

According to a modification, at step 630, based on the first and secondtime differences T_(al) and T_(d2) of the notified time-delay data, theamount of time by which the starting time of downlink data processingand transmission of the BBU is advanced equals to the sum of the averageof the difference between T_(d2) and T_(d1) for each of N periods priorto the current uplink-downlink period and the current T_(d1), wherein Nis an integer larger than 1.

According to another modification, measuring the first time differenceT_(d1) between the time when the D/A converter begins to transmitdownlink data to the mobile communication device and the time when thefirst data sample of data frame of the downlink data arrives at the RRHcan be realized through measuring, as the first time difference T_(d1),the time difference between the time when the downlink pulse T_(DL) fortriggering the D/A converter to transmit downlink data to the mobilecommunication device is generated and the time when the first datasample of the downlink frame from the BBU arrives at the downlink unit.

A pulse generator is used to generate the switching pulse T_(s) fortriggering the wireless communication system base station to switchbetween uplink mode and downlink mode, and measuring the second timedifference T_(d2) between the time when the wireless communicationsystem base station is switched from downlink mode to uplink mode andthe time when the last data sample of data frame of the downlink dataarrives at the RRH can be realized through measuring, as the second timedifference T_(d2), the time difference between the time when the pulsegenerator generates the switching pulse T_(s) for triggering thewireless communication system base station to switch between uplink modeand downlink mode and the time when the last data sample of the downlinkframe from the BBU arrives at the downlink unit.

Advancing the starting time for the BBU to process and transmit thedownlink data by an amount of time obtained based on the notifiedtime-delay data further comprises: generating a time-delayed clock pulsebased on the timing baseband processing pulse generated by the timerwithin the BBU for triggering the downlink data processing unit of theBBU to start the downlink data processing and transmission and thetime-delay data; replacing the timing baseband processing pulsegenerated by the timer with the time-delayed clock pulse to trigger thedownlink data processing unit of BBU to start the downlink dataprocessing and transmission, so that the starting time for the downlinkdata processing unit to process and transmit the downlink data isadvanced by the amount of time.

The data transmission synchronization method for the wirelesscommunication system base station of the present invention has beenoutlined above. It will be noted that, for the purpose of concise, manydetails identical or similar to that disclosed for the wirelesscommunication system base station according to the present invention areomitted. However, those skilled in the art may understand that,according to the above description of the wireless communication systembase station and its various implementations in the present invention,various implementations of the present invention can be implemented.

The present invention and some exemplary embodiments of the presentinvention have been described with reference to the drawings, however,it should be understood that, the present invention is not strictlylimited to those embodiments. Various modifications and variations canbe made by those skilled in the art without departing the scope andspirit of the present invention, and all these modifications andvariations are intended to be included in the scope of the presentinvention defined by the appended claims.

Those skilled in the art will appreciate that the present invention canbe embodied as apparatus, method and computer program product.Therefore, the present invention can be implemented, for example, whollyin hardware, wholly in software (including firmware, resident software,or microcode), or a combination of software and hardware which aregenerally called as “circuit”, “module” or “system” herein. Further, thepresent invention can be embodied as a computer program product in anytangible expression medium having computer usable program code.

Any combination of one or more computer usable or computer readablemedium(s) may be utilized. The computer usable or computer readablemedium, for example, may be, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, device, or propagation medium. More specific examples (anon-exhaustive list) of the computer-readable medium would include: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (e.g., EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a transmission media such as thosesupporting the Internet or an intranet, or a magnetic storage device.Note that the computer-usable or computer-readable medium could even bepaper or other suitable medium upon which the program is printed, as theprogram can be electronically obtained via, for instance, electronicallyscanning the paper or other medium, then compiled, interpreted, orprocessed in a suitable manner, and then stored in a computer memory ifnecessary. In the context of this document, a computer-usable orcomputer-readable medium may be any medium that can contain, store,communicate, propagate, or transport the program for use by or beassociated with the instruction execution system, apparatus, or device.The computer-usable medium may include data signal havingcomputer-usable program code embodied therein, propagated either in baseband or as part of a carrier wave. The computer usable program code maybe transmitted using any appropriate medium, including but not limitedto wireless, wire line, optical fiber cable, RF, and the like.

Computer program code for carrying out operations of the presentapplication may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++, and the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may be executed entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer, or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any types of network, including a local area network (LAN) or awide area network (WAN), or may be connected to an external computer(for example, through the Internet using an Internet Service Provider).

Further, each block of the flowchart and/or block diagrams, andcombinations of blocks of the flowchart and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which can be executed via the processor of the computer or otherprogrammable data processing apparatus, create means for implementingthe functions/operations specified in the blocks of flowchart and/orblock diagram.

These computer program instructions may also be stored in acomputer-readable medium that can instruct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instruction meanswhich implement the function/operation specified in the blocks offlowchart and/or block diagram.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions to be executed on the computer or other programmableapparatus provide processes for implementing the functions/operationsspecified in the blocks of flowchart and/or block diagram.

The flowcharts and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagram may represent a module, program segment, or aportion of codes, which comprises one or more executable instructionsfor implementing the specified logical function(s). It should also benoted that, in some alternative implementations, the functions noted inthe block may occur in an order different from the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramand/or flowchart, and combinations of blocks in the block diagram and/orflowchart, can be implemented by special purpose hardware-based systemswhich perform the specified functions or operations, or combinations ofspecial purpose hardware and computer instructions.

1. A computer-implemented data transmission synchronization method for awireless communication system base station that includes a remote radiohead (RRH) and a baseband unit (BBU) which are communicably connectedthrough a network, wherein the BBU is used to process and transmitdownlink data to the RRH, the synchronization method comprising:measuring a time-delay for the downlink data to arrive at the RRH fromthe BBU; and notifying from the RRH to the BBU of time-delay data on themeasured time-delay, wherein the time-delay data is used to advance thestarting time for the BBU to process and transmit the downlink data byan amount of time obtained based on the notified time-delay data.
 2. Thesynchronization method according to claim 1, wherein: the RRH furthercomprises a digital to analog (D/A) converter for transmitting thedownlink data to a wireless communication device, and the step ofmeasuring a time-delay for the downlink data to arrive at the RRH fromthe BBU comprises: measuring a first time difference T_(d1) between thetime when the D/A converter begins to transmit the downlink data to thewireless communication device and the time when a first data sample of adata frame of the downlink data arrives at the RRH, wherein thetime-delay data comprises the first time difference T_(d1).
 3. Thesynchronization method according to claim 2, wherein: the wirelesscommunication system base station switches between a downlink mode andan uplink mode, and the step of measuring a time-delay for the downlinkdata to arrive at the RRH from the BBU further comprises: measuring asecond time difference T_(d2) between the time when the wirelesscommunication system base station switches to the uplink mode from thedownlink mode and the time when a last data sample of the data frame ofthe downlink data arrives at the RRH, wherein the time-delay data TDfurther comprises the second time difference T_(d2).
 4. Thesynchronization method according to claim 2, wherein the amount of timeequals the first time difference Td1.
 5. The synchronization methodaccording to claim 3, wherein the amount of time equals the larger ofthe first time difference T_(d1) and the second time difference T_(d2).6. The synchronization method according to claim 3, wherein the amountof time is the sum of the average of the difference between the secondtime difference T_(d2) and the first time difference T_(d1) of each Nperiod prior to the current uplink-downlink period and the currentT_(d1), wherein N is an integer larger than
 1. 7. The synchronizationmethod according to claim 2, wherein: the RRH further comprises adownlink unit for receiving the downlink data from the BBU and a pulsegenerator for generating a downlink pulse T_(DL) for triggering the D/Aconverter to transmit the downlink data to the wireless communicationdevice, and the step of measuring the first time difference T_(d1)between the time when the D/A converter begins to transmit the downlinkdata to the wireless communication device and the time when the firstdata sample of the data frame of the downlink data frame arrives at theRRH further comprises: measuring the first time difference T_(d1)between the time when the downlink pulse T_(DL) is generated and thetime when the first data sample of the downlink frame from the BBUarrives at the downlink unit.
 8. The synchronization method according toclaim 3, wherein: the RRH further comprises a downlink unit forreceiving the downlink data from the BBU and a pulse generator forgenerating a switching pulse T_(s) for triggering the wirelesscommunication system base station to switch between the downlink modeand the uplink mode, and the step of measuring the second timedifference T_(d2) between the time when the wireless communicationsystem base station switches to the uplink mode from the downlink modeand the time when the last data sample of the data frame of the downlinkdata arrives at the RRH further comprises: measuring the second timedifference T_(d2) between the time when the switching pulse T_(s) isissued and the time when the last data sample of the downlink frame fromthe BBU arrives at the downlink unit.
 9. The synchronization methodaccording to claim 1, wherein: the BBU further comprises: (i) a downlinkdata processing unit for processing and transmitting the downlink data,and (ii) a timer for generating a timing baseband processing pulse fortriggering the downlink data processing unit to start the downlink dataprocessing and transmission, and the synchronization method furthercomprises: generating a time-delayed clock pulse to replace the timingbaseband processing pulse based on the timing baseband processing pulseand the time-delay data, so as to advance the starting time for thedownlink data processing unit to process and transmit the downlink databy the amount of time.
 10. The synchronization method according to claim3, wherein: the RRH further comprises a downlink unit for receiving thedownlink data from the BBU and a pulse generator for generating adownlink pulse T_(DL) for triggering the D/A converter to transmit thedownlink data to the wireless communication device, and the step ofmeasuring the first time difference T_(d1) between the time when the D/Aconverter begins to transmit the downlink data to the wirelesscommunication device and the time when the first data sample of the dataframe of the downlink data frame arrives at the RRH further comprises:measuring the first time difference T_(d1) between the time when thedownlink pulse T_(DL) is generated and the time when the first datasample of the downlink frame from the BBU arrives at the downlink unit.